The serial lesion effect refers to a laboratory phenomenon in which an animal that receives brain damage in several stages with an appropriate number of days between each operation does not show the deviant behaviors that may be exhibited by cage-mates that sustain the same anatomical damage in a single operation. Although this phenomenon may be related to the "effect of momentum of the lesion" that is described in the human literature on cerebrovascular disease and tumors, it has not been given the attention it would appear to deserve in the research laboratories. Nevertheless, the serial lesion effect is a replicable phenomenon. It has been demonstrated in monkeys, cats and rats, in learning and non- learning paradigms, and after subcortical as well as cortical lesions. The effect has been studied primarily in vision, but recent studies from my laboratory have noted it after cortical lesions in the somesthetic areas. The purpose of the present proposal is to examine systematically the conditions under which the serial lesion effect may appear. The proposed research concerns primarily the somatic afferent system of the rat, but the studies are not confined to this system, and the raccoon may also be used. Detailed investigations are proposed to examine factors such as the importance of training during the interlesion interval, the length of the interlesion interval necessary for sparing, and the recovery period after surgery. These experiments should, in my estimation, contribute significantly to our understanding of restitution of function, and the results may be directly applicable t human patients that must undergo neurosurgery.